It was "metal fatigue" that caused a fan blade inside the left engine of Southwest flight 1380 to break at about 30,000 feet. Within three seconds, investigators believe the engine blew and shrapnel burst out a window in the passenger cabin, killing passenger Jennifer Riordan.

New testimony just released by the National Transportation Safety Board (NTSB) says passengers rushed to help Riordan after they saw her with her seat belt still fastened, her head, torso and arm hanging out of the broken window. One even reached outside the plane to help pull her back in.

Riordan's husband spoke to CBS News days after the accident, saying if he could talk to her, he'd tell her, "I love you."

"I have no idea how I can do this without her, but because of her I know I can," he said.

The engine maker told the NTSB during a hearing Wednesday the failed engine blade had made about 32,000 flights, and was last been inspected for fatigue in 2012.

An examination of that blade after the deadly accident found signs it was likely beginning to suffer cracks from metal fatigue in 2012, but those cracks were smaller than what the tests at the time could detect.

Another Southwest Airlines 737 had an eerily similar engine failure in 2016 that prompted some additional engine inspections. Since April the FAA has issued a series of orders requiring more frequent ultrasonic inspections of fan blades on 737s.